The present invention relates generally to a method and device for an on-line automatic balancing system and more particularly to a method and device for automatically and precisely balancing machine rotors during rotation.
The prior art teaches compensation of an unbalance in a rotor, but the rotor must be stopped before the balancing operation can proceed. Therefore, balancing operations have to be repeated at intervals, which is very time-consuming, and the results may not be very accurate.
Take a grinding machine for an example. When its grinding wheel is applied on a workpiece, even though the machine has previously been stopped and balanced, continuous wear on the surface of the wheel during the grinding process will cause a new unbalance and generate greater vibrations of the machine, affecting the precision of surface finish. Therefore, it is necessary to stop the machine at intervals to replace or balance the grinding wheel. This is often time-consuming and the machining process must be temporarily stopped. However, if the unbalance signal of the grinding machine is monitored at fixed intervals or at random for just a few minutes (1-3 minutes) during the grinding process so that the balancing operation is initiated when the unbalance value is measured to be greater than a predetermined tolerance value, then it is not necessary to stop the machine. Once the balancing operation is over, the grinding process can then continue. Thus, a high and stable quality of surface finish can be achieved and efficiency can also be increased. In view of this, it is indeed necessary to develop a precise automatic dynamic balancing device.
According to the inventors' research, there is only one pertinent patent in this field, that is, U.S. Pat. No. 4,688,355 issued Aug. 25, 1987, entitled "Method and Apparatus for Continuous Compensation of Grinding Wheel Unbalance." This patent teaches a device which adopts an analog signal processing method. It uses a broadband filter, a phase control rectifier to control the water output of the valve device and to measure the amount and location of unbalance. But this device has the following setbacks:
1. The transmitted signals are not clear: The vibration signals are usually caused by several vibration sources, such as unbalance, misalignment, motor, etc. By using a broadband filter for signal processing, the time domain signals are not pure enough to enable the system to judge the input unbalance signals.
2. Measurement of unbalance in grinding wheels is not precise: Because the measured analog signals contain several other vibration signals mentioned above, and the true unbalance signal cannot be separated by a broadband filter, the magnitude and location of unbalance of a rotor cannot be precisely determined by this system.